Certain uses of power cable (e.g., electrical, hydraulic, etc.) are in extremely adverse environments wherein the cable is subjected to extreme heat and large mechanical forces such as stress and crushing forces. One example of such an adverse environment is oil wells wherein a power cable runs from a surface power source down to equipment at the bottom of the oil well. Such oil wells can have depths of many thousands of feet. This cable is usually comprised of a plurality of conductor assemblies arranged in a single bundle. Each conductor assembly has a center conductive core element or filament surrounded by a layer of insulation.
This cable is commonly banded or otherwise affixed to the oil well tubing, commonly known as the "production tubing", which runs the depth of the well hole. These bands, straps, or other fastening members may crush the cable and thereby seriously degrade the effectiveness of the insulation of the cable and the strength of the cable. These cables are also subjected to impact damage during installation and retrieval of the production tubing, particularly when the cable is being employed in a deviated well hole, that is, a well which is not perfectly straight. For example, the cable may be crushed between the production tubing and the side of the well hole liner (commonly known as the "casing") as it is inserted or removed from the well hole.
In view of these adverse conditions, it has become conventional for cables that are to be employed in environments such as oil wells to be wrapped with an armor covering. In addition, the layers of insulation surrounding the individual conductors of the cable are selected for their optimum electrical, chemical and mechanical characteristics.
Often, these adverse environments also involve severe space limitations on the size of the cable which can be employed. This is particularly true of oil wells wherein the space between the production tubing and the casing and the size of the cable is critical. In view of these size limitations, it is advantageous to use a "flattened out" cable in these environments. A "flattened out" cable has two or more conductor assemblies forming a row. Typically, these cables involve three conductor assemblies arranged in a single row. While this design may overcome some of the problems with space limitations, the cable is still subjected to the possibly damaging mechanical forces discussed above.
To prevent the "flattened out" cable from being damaged by these mechanical forces, cable designs have been developed which have internal structural members located within the armor covering and between the individual conductor assemblies. Examples of these cables are disclosed in U.S. Pat. Nos. 4,409,431 issued to David H. Neuroth (a co-inventor of this invention) on Oct. 11, 1983; 4,453,035 issued to David H. Neuroth on June 5, 1984; 4,453,036 issued to David H. Neuroth on June 5, 1984; 4,454,377 issued to David H. Neuroth on June 12, 1984; 4,454,378 issued to David H. Neuroth on June 12, 1984; 4,490,577 issued to David H. Neuroth on Dec. 25, 1984; 4,532,374 issued to David H. Neuroth on July 30, 1985; 4,539,739 issued to John E. Himmelberger and James O. Scharf on Sept. 10, 1985; 4,572,926 issued to Robert Ganssle et al. on Feb. 25, 1986; and British Pat. No. 699,558 entitled "Improvements in or Relating to Electric Cables" and issued on Nov. 11, 1953.
While the cables disclosed in these patents have increased resistance to external mechanical crushing forces, additional problems have arisen because the numerous structural support members used have added additional weight and cost to the cable. In applications where great lengths of the cable are employed, such as in an oil well, this additional weight is a disadvantage as it adds to the weight of the production tubing and cable assembly which must be raised and lowered into the drill hole. This additional weight puts additional stress on the equipment used to transport the cable and to raise and lower the production tubing and cable and thus may slow the drilling operation. In addition, the use of numerous internal structural support members greatly adds to the material costs and manufacturing expenses for such highly reinforced cables.
Thus, there is a need in the art for a power cable for adverse environments which is resistant to external crushing forces such as the crushing forces of the banding operation which are present even in non-deviated holes, and yet is relatively lightweight and cost-effective. There is always a need in certain environments such as oil wells for a lightweight, strong and cost-effective power cable.
This invention fulfills these needs in the art, as well as other needs which become apparent to those skilled in the art once given this disclosure, by providing a power cable as disclosed herein.